Field of the Invention
The present invention relates to a wafer processing method.
Description of the Related Art
There has been put into practical use a manufacturing method for a semiconductor wafer having a plurality of semiconductor devices such as ICs and LSIs, wherein the semiconductor wafer is intended to improve the processing performance of the semiconductor devices. This semiconductor wafer is composed of a substrate and a functional layer formed on the front side of the substrate, wherein the functional layer is formed by stacking a plurality of low-permittivity insulator films (low-k films). Examples of each low-k film include an inorganic film of SiOF, BSG (SiOB), etc. and an organic film such as a polymer film of polyimide, parylene, etc. The semiconductor devices are formed from the functional layer of the wafer. The functional layer is brittle so that it is easily separated from the substrate in cutting the wafer by using a cutting blade. To cope with this problem, there has been performed a wafer processing method including the steps of applying a laser beam along both sides of each division line on a semiconductor wafer to form two laser processed grooves dividing the functional layer along each division line, and next positioning a cutting blade between the two laser processed grooves along each division line to relatively move the cutting blade and the semiconductor wafer, thereby cutting the wafer along each division line (see Japanese Patent Laid-Open No. 2005-64231, for example).
However, this wafer processing method has the following problems. Since the functional layer is divided in the condition where the spacing between the two laser processed grooves is larger than the width of the cutting blade, laser scanning must be performed plural times along each division line, causing an increase in processing time. Further, uneven wearing of the cutting blade may occur depending upon the shape of the laser processed grooves formed along each division line. Further, a protective film must be formed on the front side of the wafer, so as to prevent the adhesion of debris generated in laser processing. Further, a passivation film of SiO2, SiN, etc. is formed on the front side of the functional layer. Accordingly, when a laser beam is applied to the wafer from the front side thereof, the laser beam passes through the passivation film to reach the inside of the functional layer, causing passable damage to the devices.
To cope with these problems, the prevent applicant has proposed a processing method for a wafer including a substrate and a functional layer formed on the front side of the substrate, wherein the substrate of the wafer is cut from the back side thereof along each division line by using a cutting blade to form a cut groove having a depth not reaching the functional layer with a part of the substrate left between the bottom of the cut groove and the functional layer, and the functional layer is next removed by applying a laser beam to the bottom of the cut groove or by performing plasma etching.